• Aerospace Engineering and Technology
• /
• v.10 no.2
• /
• pp.1-10
• /
• 2011

This is a comparative study of three inertia navigation units and focuses on the verification of reliability about GPS/INS for the SmartUAV(DGNS). Those GPS/INS have been tested using a manned aircraft and an automobile. The comparative aspect of units include details about the GPS positions and the inertia sensor performance. With the flight scenario, the DGNS guarantees the reliability of the navigation operation and performs the flight test for the development of the SmartUAV.

• Current Industrial and Technological Trends in Aerospace
• /
• v.7 no.1
• /
• pp.119-127
• /
• 2009

There have been about 450 atomic frequency standards (or atomic clocks) launched into orbit for the use on communications and scientific payloads since 1970's. GPS satellites carry on-board Rubidium and Cesium atomic frequency standards which are utilized for the precise positioning and timing. The evolving technologies of space qualified atomic frequency standards have enhanced in the performance, reliability, and lifetime of satellites. In this paper we describe the fundamentals and performance of the atomic frequency standards, and introduce the atomic frequency standards which are presently on-board various satellites systems. We also present the GPS time scale and its applications.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.42 no.6
• /
• pp.505-514
• /
• 2014

The effects of reflected wave of the sea on pseudolite ranging accuracy are analysed in this paper, when a pseudolite navigation system is used for wide area outdoor applications such as aircraft and vessels positioning. Methods for minimizing the influence of sea surface reflection wave were proposed. The methods include the appropriate correlator in pseudolite navigation system through the correlation performance comparison analysis in receiver design, the use of the technology of multiple antennas, and locating the transmitting station antenna on an appropriate position. From the results of experiments, the method of locating the antenna position shows the most reliable performance against the effect of surface reflection wave. The analysis results of the ranging accuracy improvement are addressed, when the multipath caused by sea surface reflection exists.

• Journal of Space Technology and Applications
• /
• v.4 no.3
• /
• pp.232-243
• /
• 2024

In order to perform various missions in space, including planetary exploration, estimating the position of a satellite in orbit is a very important factor because it is directly related to the success rate of mission performance. As a study for autonomous satellite navigation, this study estimated the satellite's attitude and real time orbital position using a star sensor algorithm with two star trackers and earth sensor. To implement the star sensor algorithm, a simulator was constructed and the position error of the satellite estimated through the technique presented in the paper was analyzed. Due to lens distortion and errors in the center point finding algorithm, the average attitude estimation error was at the level of 2.6 rad in the roll direction. And the position error was confirmed by attitude error, so average error in altitude direction was 516 m. It is expected that the proposed satellite attitude and position estimation technique will contribute to analyzing star sensor performance and improving position estimation accuracy.

• Journal of Advanced Navigation Technology
• /
• v.12 no.6
• /
• pp.567-573
• /
• 2008

According to the ICAO's Global Air Navigation Plan for CNS/ATM - Communications, Navigation, and Surveillance - systems, employing digital technologies, including satellite systems together with various levels of automation, are to be applied in support of a seamless global air traffic management system. For the future navigation, the focus of future implementation efforts can be placed entirely on an expected gradual migration toward GNSS-based navigation, Korea has been considered various options for airspace GNSS augmentation system: GBAS, SBAS and GRAS. This paper discusses current status and future trend of GNSS airspace navigation systems, and presents the results of possible augmentation options and scenarios to analyze system availabilities which could lead to the conclusion of the best program for Korea. The results showed that Korea could have sufficient availabilities from en-route to CAT-I approach with ABAS and GBAS. The study was in cooperated with MITRE, an American research company.

• Current Industrial and Technological Trends in Aerospace
• /
• v.8 no.1
• /
• pp.77-85
• /
• 2010

The current GPS constellation consists of 32 Block IIA/IIR/IIR-M satellites including 12 Block IIA satellites on service over 15 years. The satellites in poor space conditions may suffer from anomalies, especially influenced by aging atomic clocks which are of importance positioning and timing. Recently, the IGS Ultra-rapid predicted products have not shown acceptably high quality prediction performance because the Block IIA cesium clocks may be easily affected by various factors such as temperature and environment. The anomalies of aging clocks involve lower performance of positioning in the GPS applications. We, thus, describe satellite clock behaviors and anomalies induced by aging clocks and their detection technologies to avoid such anomalies.

• Journal of Satellite, Information and Communications
• /
• v.9 no.2
• /
• pp.119-125
• /
• 2014

In this paper, we developed the signal generator of GNSS navigation signals and analysis the performance of DCO(Digitally Clock Oscillator) compensation algorithm for cumulative distance error thorough simulation. In general, To generate a GNSS signal calculates the Doppler and Initial Pseudorange by using the location information of the receiver and the satellite. The GNSS signal generator generates a signal by determine the carrier and code output frequency using the Doppler information which is calculated as a function of time. The output frequency of the carrier and code would be used the DCO scheme. At this time, It extract the bit and code information on a for each sample by accumulating the DCO. an error of Pseudorange is generated by the cumulative error of the DCO. If Pseudorange error occurs, so that the influence to and operation of the receiver. Therefore, in this paper, we implemented the accumulated error compensation algorithm of the DCO to remove the accumulated error components DCO thereof, Pseudorange accumulated error is removed through the experiment, it was confirmed to be a high accuracy can be operated.

• Current Industrial and Technological Trends in Aerospace
• /
• v.5 no.1
• /
• pp.3-11
• /
• 2007

1990년대 초부터 2000년대 중반까지 구소련의 붕괴와 예산 투자의 저조로 정체기에 접어들었던 우주개발은 달 및 행성탐사와 같은 새로운 연구개발 움직임과 중국, 인도 등 새로운 우주강자의 부상으로 현재 신성장기를 맞이하고 있는 것으로 보인다. 전 세계 우주프로그램의 정부투자도 2006년 총 50.36 십억 달러로 역사상 최고점을 기록하고 있기도 하다. 주요 우주개발국들은 미국의 우주탐사 계획에 버금가는 탐사계획들을 잇따라 발표했으며, GPS, GLONASS, Galileo 등 위성항법 분야 연구개발에도 높은 우선순위를 부여하고 있다. 정부의 연구개발 투자 확대는 우주산업의 활성화에 직접적으로 영향을 미치는 요인이 된다. 실제로 미국 우주산업 매출의 90%가, 그리고 유럽 우주산업 매출의 60%가 정부고객으로부터 발생하고 있다. 2005년 우주산업 매출은 총 88.8 십억 달러로 전년대비 6% 정도 성장하였으며, 여전히 위성서비스 분야가 전체 매출에서 차지하는 비중이 60%로 가장 높다. 본고에서는 우주분야의 정부 예산 투자 현황과 우주탐사 및 위성항법을 중심으로 한 새로운 연구개발 움직임을 국가별로 살펴보고, 우주산업의 동향과 전망, 그리고 우리나라의 우주산업과 우주개발 관련 주요 정책변화, 현재 진행 중인 국가 우주개발 프로그램에 대해 간략하게 살펴보도록 하겠다.

• Journal of Advanced Navigation Technology
• /
• v.19 no.6
• /
• pp.499-506
• /
• 2015

Global navigation satellite systems (GNSS) is operating widely in civil and military area. GNSS signals, however, can be easily interfered because its signal is vulnerable to jamming. Thus, a sort of backup or alternative system is needed in order that the navigation performance is assured to a certain degree in case of GNSS jamming. In order to suggest a series of backup or alternative system of regional navigation, in this paper, we introduced a high altitude long endurance unmanned aerial vehicle (HALE UAV) with pseudolites using inverted GPS and transceiver system. We simulated the positioning error of the regional navigation system using HALE UAV with inverted GPS or transceivers concepts. We estimated the position error of HALE UAV calculate user position errors based on the position error of HALE UAV and general pseudorange error.

• Journal of Satellite, Information and Communications
• /
• v.7 no.1
• /
• pp.128-133
• /
• 2012

In this paper, we analysis the effect of error of code tracking and frequency tracking according to the chip delay of spoofing signal through the simulation. Firstly, we investigate the type of spoofing signal and defense technical of spoofing attack. For simulation, we generated the intermediate spoofing signal using the software GNSS signal generator simulator(SGGS), the intermediate spoofers synchronize its counterfeit GPS signals with the current broadcast GPS signals. The software GPS receiver simulator(SGRS) received the spoofing signal and normal signal from SGGS, and process the signals. In paper, we can check that the DLL and PLL tracking loop error are generated and pseudo-range is changed non-linear according to chip delay of spoofing signal when the spoofing signal is entered. As a result, we can check that navigation solution is incorrectly effected by spoofing signal.